1. Technical Field
The present invention relates to a method for forming a micro-pattern of a semiconductor device, and more particularly, to a process for preventing defects in a photoresist pattern, such as footing or undercut occurred in using organic anti-refective coatings.
2. Description of the Related Art
With an increase in integration density of a semiconductor device, lithographic techniques are becoming the key to the realization of highly integrated memory devices. Particularly, a process for forming a photoresist pattern is a very important process in fabricating a semiconductor apparatus.
Generally, a photoresist pattern depends on an exposure process. In the exposure process, the photoresist pattern is greatly affected by light reflected by a bottom semiconductor substrate. In order to solve this problem, an anti-reflective layer is additionally formed prior to the process for forming a photoresist pattern.
As a widely-known anti-reflective layer, an inorganic SiON layer is a bottom anti-reflective layer(BARL) commonly used in the lithographic process using a KrF line.
However, in an etching process, a problem occurs in the etching selectivity of an inorganic SiON layer to a semiconductor substrate. If an unnecessary inorganic SiON layer remains on the semiconductor substrate after the etching process, it affects the performance of the device, thereby requiring the inconvenience of removing it completely.
In addition, in the case that a transparent silicon oxide layer with a complex stepped portion is formed on the bottom semiconductor substrate, the thickness of the formed inorganic SiON layer is not uniform in all parts thereof, and thus the intensity of a reflected light on the bottom semiconductor substrate is non-uniform.
In addition, since the inorganic SiON layer is sensitive to oxygen in air and forms a non-uniform, thin oxide layer after a lapse of time, it generates defects in a chemically amplified resist (CAR) to be formed on an upper portion of the inorganic SiON layer, thereby causing the inconvenience of removing the oxide layer by an oxygen plasma process.
On the other hand, in late-nineties, as the chemically amplified resist obtained a high transmittance to overcome resolution limitations, a problem occurs in that a photoresist pattern is deteriorated on a highly reflective substrate. In such a circumstance, limitations in using only the inorganic SiON layer as an anti-reflective layer result.
Hence, anti-reflective coating materials capable of functioning as an inorganic SiON layer or replacing it have been developed. As a result, organic anti-reflective coating materials that had been developed in mid-nineties, but have rarely been used because of little need for it, are being used again recently.
These organic anti-reflective coatings dramatically have increased etching speed by using metacrylate resins, rather than prior art resins containing benzene radical. Techniques have been developed for using methacrylate resins as anti-reflective coatings even at a thickness of less than 1000 xc3x85. In addition, by cross-linking the insides of the organic anti-reflective coatings having a small thickness with each other so that the surfaces of the organic anti-reflective coatings are hardened by using a thermal acid generator (TAG) compound, it is possible to develop techniques for adjusting compatibility at the interface with photoresists formed on the upper portion of the organic anti-reflective coating.
However, in the case of using the above-described organic anti-reflective coatings, a problem occurs about matching with respect to some parts of the photoresists. In other words, inter-mixing between the organic anti-reflective coating and the photoresist often occurs according to its manufacturer, thereby generating defects in a photoresist pattern, such as (a) footing or (b) undercut as shown in (a) of FIG. 1 and (b) of FIG. 2.
A method is disclosed for preventing defects in a photoresist pattern, such as undercut or footing, due to inter-mixing between an organic anti-reflective coating and a photoresist by forming a carbonized layer on the top surface of the organic anti-reflective coating by a curing process like ion implantation or E-beam curing.
A method for forming a micro-pattern of a semiconductor device is disclosed which comprises: forming an organic anti-reflective coating on the top of a semiconductor substrate and carrying out a hard-baking process; carrying out a curing process on the organic anti-reflective coating to form a carbonized layer thereon; coating a photoresist on the top of the carbonized layer and carrying out a soft-baking process; carrying out exposing and developing processes on the substrate coated with the photoresist to form a photoresist pattern; and washing the resultant material.